A system of inorganic chemistry / by William Ramsay.

Date:
1891
Catalogue details

Licence: Public Domain Mark

Credit: A system of inorganic chemistry / by William Ramsay. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    699/740 (page 687)
    RECOVERY OF MANGANESK allowed to settle, and the clear liquor is mixed witli milk of lime free from magnesia. This precipitates manganese hydroxide, Mu(0H)2, and the object of the process is to convert this hyd]- oxide into hydrated dioxide by means of a blast of air. If an- were blown through such moist hydroxide at a high temperatnrf, only one-third of the manganese would be oxidised, the product being hydrated Mn304, which may be viewed as Mn02.2]VlnO; at the ordinary temperature the action would be very slow, and would lead to the formation of MnoOg = MnOs-MnO. But if excess of lime be added in addition to that required to precipitate manganous hydroxide, and if the mud of hydroxides of manganese and calcium be exposed to air in a hot state, a mixture of man- ganites of calcium, of the formulae Ca0.2Mn02 and CaO.MnOo, is formed, in which all manganese is in the state of peroxide. The presence of calcium chloride in the b'quid is desirable, inasmuch as it is then better able to dissolve lime, and to bring about its combination with the peroxide.. The mud is placed in tall iron, cylinders, and heated by blowing in steam ; air is then forced in. The temperature should, not exceed 65°, else MrxJDi and MnjOg are formed. The manganese rapidly oxidises, and the colour of the mud changes to black. When the amount of dioxide no longer increases, manganous chloride is rua in, when the reaction occurs :— 2(CaO.Mn02) + MnCla. + HoO = Ca0.2Mn02 + Mn(0H)2 + CaClc. The mud is then run into tanks and the calcium chloride drawn off from the precipitated sludge. A diiferent form of chlorine still, taller in proportion to its diameter, and unprovided with a grating, is made use of. It is charged with hydrochloric acid, and the mud is run in as long as chlorine is evolved; the mixture grows hot, and nearly all the hydrochloric acid may be utilised, only | to 1 per cent., remaining free at the end of the reaction. It is advisable to employ the acid liquor from the stills charged with manganese ore along with fresh hydrochloric acid in the mud stills; the free acid is thus saved. Another process of manganese recovery, practised on a limited scale, is due to Mr. Dunlop. It consists in converting the man- ganous chloride into carbonate by heating its solution under pressure with chalk; the calcium chloride is removed, and the precipitated manganous carbonate, while still moist, heated in a